JP2009300244A - Corrosion sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a corrosion sensor which shows less power consumption and is capable of measuring a degree of corrosion without being affected by temperature, density and viscosity. <P>SOLUTION: The corrosion sensor is equipped with a corrosion chip fixed to one end of a non-corrosive first elastic body, a non-corrosion chip fixed to one end of a non-corrosive second elastic body, a self-oscillation circuit for respectively resonating the corrosion chip and the non-corrosion chip through the first and second elastic bodies, a frequency counter for counting the resonance frequency from the corrosion chip and the non-corrosion chip, and an arithmetic part for operating the ratio of the square of frequency. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a corrosion sensor that detects corrosion of a structural member, and corrodes a corrosive member and a non-corrosive member and corrosives that estimate the degree of corrosion of the member to be measured based on the difference in resonance frequency of these members. It relates to sensors.

  Conventionally, there are known corrosion sensors that measure corrosion weight loss by increasing electrical resistance and those that measure electrochemical potential. The corrosion weight loss method measures the electrical resistance, but the electrical resistance corresponding to the shape change is measured, so the voltage may affect the corrosion chemical reaction.

The high-sensitivity electrical resistance method is used in field verification tests because it can monitor the corrosiveness of the environment as the corrosion rate and is excellent in sensitivity and responsiveness.
Moreover, also known corrosion sensor by chemical potential, the corrosion sensor CL ^- can not predict exactly corrosion occurs because such is influenced by ions present in the environment. For example, when CL ^- is present, pitting corrosion occurs in the passive region, and iron is pierced. The potential-pH diagram cannot predict all phenomena that occur in the actual environment.

FIG. 2 shows a conventional example of a corrosion sensor that detects a resonance frequency that changes due to corrosion and measures the degree of corrosion of a measurement member.
The corrosion sensor includes a disk-shaped measurement sample 11, a rigid cylindrical support 12 that fixes the periphery of the measurement sample 11, a vibrator 13 that fixes and attaches the end of the support 12, It is composed of a physical quantity sensor 14 installed in the back of the measurement sample or in the vicinity thereof in a sealed space surrounded by the measurement sample 11, the support 12 and the vibrator 13.

In the above configuration, first, the vibrator 13 is vibrated by an external signal, and the vibration is propagated in the direction perpendicular to the surface of the measurement sample 11 via the support 12. The physical quantity sensor 14 measures the amplitude.
Here, the physical quantity sensor 14 measures the distortion, displacement, electric capacity, etc. of the measurement sample 11 in contact or non-contact, and the measurement value is converted into an electric signal and taken out to the outside.

FIG. 3 is a block diagram of such a corrosion sensor.
In the figure, the corrosion sensor 1 is shown in FIG. 2, and the measurement sample 11 of the corrosion sensor 1 vibrates through the support 12 in accordance with the vibration of the vibrator 13 driven by the vibrator drive circuit 2, and the measurement sample. 11 is measured by the physical quantity sensor 14. The measured vibration data is input to the computer 3 and processed.

When the sweeping vibration that varies with frequency high → low or low → high corrosion sensor 1 by the vibrator driving circuit 2, the corrosion sensor 1 resonates when it reaches a resonant frequency of the respective orders .
4A and 4B show the vibration characteristics of the measurement sample 11 in the corrosion sensor 1. The horizontal axis indicates the frequency of vibration applied to the measurement sample, and the vertical axis indicates the measurement sample 11 with respect to the frequency. The amplitude of is shown.

The solid curve indicates the vibration characteristics when the measurement sample changes in mass due to corrosion or the like, and the chain line curve indicates the vibration characteristics when the measurement sample is in the initial new state. As shown in these figures, the amplitude of the measurement sample 11 reaches a peak at the resonance frequency. At the time of measurement, the physical quantity corresponding to the amplitude of the measurement sample 11 is input from the physical quantity sensor 14 installed in the corrosion sensor 1 at each frequency, and the vibration frequency of the excitation force is input from the vibrator driving circuit 2 to the computer 3 at the time of measurement. The frequency corresponding to the peak of the physical quantity is determined as the resonance frequency.

  Next, when the mass of the measurement sample 11 is apparently increased due to corrosion product deposits or deposits, the resonance frequency P0 ′ at each order of the measurement sample damaged as shown in FIG. P1 ′ and the like shift to a higher frequency side than the resonance frequencies P0 and P1 when there is no mass change in the initial stage. Further, when the mass of the measurement sample decreases due to elution and dissolution, as shown in FIG. 4B, the resonance frequencies P0 ″, P1 ″, etc. in each order of the measurement sample damaged are the initial masses. It shifts to the lower frequency side compared to the resonance frequencies P0, P1, etc. when there is no change.

  Therefore, the difference between the resonance frequency at the initial stage of the measurement sample 11 in the computer 3 and the resonance frequency after the mass change occurs in the measurement environment is obtained, the measurement sample corresponding to the value is calculated, and the corrosion damage is quantified. It can be done at any time. In the lowest resonance vibration among the resonance frequencies of each order, the amplitude peak of the measurement sample is the largest compared to the other higher-order amplitude peaks, and the amplitude peak can be detected.

JP-A-3-183946

Incidentally, the above-described conventional example has the following problems.
Since the frequency is swept up to the maximum amplitude, or when the phase difference between the excitation signal of the oscillation circuit and the vibration signal of the vibrating body is π / 2, the frequency is found as the resonance frequency. Power consumption and a predetermined time.
Further, since vibration is affected by temperature, viscosity, and density, correction is necessary.

  Accordingly, an object of the present invention is to provide a corrosion degree sensor that consumes less power and can measure the corrosion degree without being affected by temperature, density, and viscosity.

The present invention has been made to solve the above problems, and in the invention according to claim 1,
A corrosive tip fixed to one end of the non-corrosive first elastic body, a non-corrosive tip fixed to one end of the non-corrosive second elastic body, and the corrosive tip via the first and second elastic bodies And a self-oscillation circuit that resonates the non-corrosive chip, a frequency counter that counts the resonance frequency from the corrosive chip and the non-corrosive chip, and a calculation unit that calculates a ratio of the squares of the two resonance frequencies. It is provided with.

In claim 2, in the corrosion sensor according to claim 1,
The corrosive tip and the non-corrosive tip are formed to resonate at the same frequency in the initial stage.

In claim 3, in the corrosion sensor according to claim 1,
The first and second elastic bodies are subjected to a rust treatment including rust steel or gold plating.

In claim 4, in the corrosion sensor according to claim 1,
The corrosive chip and the non-corrosive chip are arranged close to each other in the environment where the structure whose corrosion degree is to be measured is arranged, and the corrosive chip is formed of the same member as the member whose corrosion degree is to be measured. It is characterized by that.

  As is apparent from the above description, according to claim 1 of the present invention, the corrosion tip fixed to one end of the non-corrosive first elastic body and the non-corrosion fixed to one end of the non-corrosive second elastic body. A corrosion chip, a self-oscillation circuit that resonates the corrosive chip and the non-corrosive chip via the first and second elastic bodies, and a resonance frequency from the corrosive chip and the non-corrosive chip are counted. Since it has a frequency counter and a calculation unit that calculates the ratio of the squares of the two resonance frequencies, the power consumption is low and the corrosion degree of the corrosive chip is measured without being affected by temperature, density, and viscosity. Can do.

  According to the second aspect, since the corrosive tip and the non-corrosive tip are formed so as to resonate at the same frequency in the initial stage, the state of corrosion can be easily observed continuously.

According to the third aspect, since the first and second elastic bodies are subjected to rust treatment including rust steel or gold plating, it is possible to obtain a highly reliable corrosion sensor without noise.
Further, according to claim 4, the corrosive tip and the non-corrosive tip are arranged close to each other in the environment where the structure whose corrosion degree is to be measured is arranged, and the corrosive tip should measure the corrosion degree. Since it is formed of the same member as the member, it is possible to monitor the corrosion of the structure with high reliability.

FIG. 1 is a block diagram showing an example of an embodiment of a corrosion sensor according to the present invention.
In FIG. 1, reference numeral 21 denotes a corrosive chip, which is formed of the same material as the member whose corrosion degree is to be measured. Reference numeral 22 denotes a non-corrosive (corrosion resistant) chip that functions as a reference.

  The dimensions of these chips are, for example, 10 × 20 mm in length and width and about 5 mm in thickness, and are fixed to one end of non-corrosive springs (hereinafter simply referred to as springs) 22 a and 22 b having a length of about 50 mm and a diameter of about 3 mm. Reference numerals 24a and 24b denote fixing members, which are formed to have a diameter of 10 mm and a length of 10 mm, for example, and the other ends of the springs 22a and 22b are airtightly fixed to one end thereof.

  25a and 25b are known self-excited oscillation circuits composed of piezoelectric elements, coils, etc., and their outputs are transmitted to the corrosive chip 21 and the non-corrosive chip 22 via the springs 22a and 22b, and these chips resonate. Resonate with frequency.

  Reference numeral 26 denotes a CPU including a frequency counter 27, which inputs the resonance frequencies of the corrosive chip 21 and the non-corrosive chip 22 and calculates the square ratio of the two resonance frequencies. As shown in FIG. 1, the fixing member 24 (a, b) is hermetically fixed to the wall surface indicated by the alternate long and short dash line A, for example, and corrodes the corrosive tip 21 and the non-corrosive tip 22 including the springs 23a, 23b. It is arranged close to the environment (for example, in the liquid) where the structure whose degree is to be measured is arranged.

In the above-described configuration, the corrosive tip and the non-corrosive tip (reference) have the same shape, and the mass Mc and the mass Mr are also the same, and the spring constants of the non-corrosive springs 23a and 23b formed in the same material and the same shape are represented by K. Then,
The frequency f of the non-corrosive chip (reference) can be expressed by the following formula.
fr = 1 / 2π · (K / Mr) ^1/2
Further, the frequency fc of the corrosive chip is represented by the following expression.
fc = 1 / 2π · (K / Mc) ^1/2

Therefore, (fr / fc) ² = Mc / Mr.
Before the corrosion proceeds, (fr / fc) ² is equal to 1.
As the corrosion progresses, the amount of Mc decreases, so the degree of corrosion can be known.
The corrosion rate can be calculated by d [(fr / fc) ² ] / dt.

Although fc = 1 / 2π · (K / Mc) ^1/2 can be measured from a decrease in Mc, the effective spring constant K changes due to the influence of fluid viscosity, temperature, etc., so that fc changes ( fr / fc) ² makes the weight loss non-dimensional, reduces the error, and reduces the influence of temperature and viscosity.

According to the above configuration,
(1) Corrosion sensor that detects the decrease in mass, which is the actual corrosion amount regardless of the corrosion potential, as a change in the frequency of the electromechanical resonance circuit.
(2) Mass loss due to corrosion can be measured continuously,
(3) By calculating the frequency ratio between the corroding vibrator and the reference vibrator that does not corrode, a corrosion sensor that outputs corrosion weight loss and corrosion rate can be realized.

  According to the article of known literature, piping technology 8086 anticorrosion inhibitor, the corrosion rate of the distillation column of the oil refining process is set to about 0.01 mm / year. For example, even if the corrosion rate is 10 times faster than this, the corrosion rate is about 0.1 mm / year. Therefore, if the thickness of the corrosive chip is about 5 mm, it functions sufficiently as a corrosion-resistant sensor.

Looking at the change in frequency as (fr / fc) ² = Mc / Mr,
Since Δ (fc / fc) ² = Δ (Mc / Mc), if the resolution is 0.01% (1/1000) in frequency, the corrosion degree of the corrosion chip of 0.02% can be detected.
That is, if the thickness of the corrosion tip is 5 mm, a change (corrosion) of 5 mm × 0.0002 = 0.001 mm can be detected.

The above description merely shows a specific preferred embodiment for the purpose of explanation and illustration of the present invention. In the embodiment, the shape of the corrosive / non-corrosive chip is rectangular, but the shape is not limited to the illustrated example. Further, the shape of the spring may be a round bar, and it may be any shape and material that resonates at the natural frequency.
Therefore, the present invention is not limited to the above-described embodiments, and includes many changes and modifications without departing from the essence thereof.

It is a block diagram which shows an example of embodiment of the corrosion sensor of this invention. It is a block diagram of the conventional corrosion sensor. It is a block diagram of the conventional corrosion sensor. It is a figure which shows the vibration characteristic of the measurement sample in the conventional corrosion sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Corrosion sensor 2 Vibrator drive circuit 3 Computer 11 Measurement sample 12 Support body 13 Vibrator 14 Physical quantity sensor 21 Corrosive chip 22 Non-corrosive chip 23 Spring 24 Fixing member 25 Self-excited oscillation circuit 26 CPU
27 Frequency counter

Claims (4)

  A corrosive tip fixed to one end of the non-corrosive first elastic body, a non-corrosive tip fixed to one end of the non-corrosive second elastic body, and the corrosive tip via the first and second elastic bodies And a self-oscillation circuit that resonates the non-corrosive chip, a frequency counter that counts the resonance frequency from the corrosive chip and the non-corrosive chip, and a calculation unit that calculates a ratio of the squares of the two resonance frequencies. Corrosion sensor characterized by comprising.   The corrosion sensor according to claim 1, wherein the corrosive chip and the non-corrosive chip are formed to resonate at the same frequency in an initial stage.   The corrosion sensor according to claim 1, wherein the first and second elastic bodies are subjected to an antirust treatment including nonrust steel or gold plating.   The corrosive chip and the non-corrosive chip are arranged close to each other in the environment where the structure whose corrosion degree is to be measured is arranged, and the corrosive chip is formed of the same member as the member whose corrosion degree is to be measured. The corrosion sensor according to claim 1.

Images